Square lite projector using prismatic lens

ABSTRACT

A reflector and lens projecting assembly is adapted to project a rectangular or square pattern of light from a conventional circular reflector. A prismatic lens having four 90* segments is positioned in front of the reflector and directs the light from the reflector into four mutually over-lapping segments in which radii of the unmodified pattern from the reflector form the boundaries of the square or rectangular pattern as modified by the lens. Embodiments are shown using light modifying prisms in which the thick portions of the prism are at the periphery of the lens and in which the thick portions of the prism are at the center of the lens.

United States Patent 1 1 Nordquist, deceased [451 May 8, 1973 [75]Inventor:

[73] Assignee: Grimes Manufacturing Company,

Urbana, Ohio [22] Filed: June 16, 1971 [21] Appl. No.2 153,642

521 U.S.Cl. ..240/41.3,240/7.4, 240/1061 51 rm.c| ..F2lv 13/04 [58]FieldotSearch ..240/41.3,7.4,41.15,

[56] References Cited UNITED STATES PATENTS 1,350,295 8/1920 Champeau..240/106. 1 X 2,366,356 1/1945 Rolph ..240/93 Hamel et al. ..240/93Foulke ..240/106 R Primary Examiner-Richard L. Moses Attorney-Marechal,Biebel, French & Bugg [57] ABSTRACT A reflector and lens projectingassembly is adaptcd to project a rectangular or square pattern of lightfrom a conventional circular reflector. A prismatic lens having four 90segments is positioned in front of the reflector and directs the lightfrom the reflector into four mutually over-lapping segments in whichradii of the unmodified pattern from the reflector form the boundariesof the square or rectangular pattern as modified by the lens.Embodiments are shown using light modifying prisms in which the thickportions of the prism are at the periphery of the lens and in which thethick portions of the prism are at the center of the lens.

9 Claims, 10 Drawing Figures PATENTEDNAY am: 3.132.41 7

sum 2 0F 3 FIG-4 LLl [T5 PATENTED A 3.732.417

SHEET 3 BF 3 FIG-6 I '2 FIG-7 2 I 3 so 4 I Q If i B 5A B I A so FOCALPOINT \OF ELLIPSE V AXIS 52 I l SQUARE LITE PROJECTOR USING PRISMATICLENS BACKGROUND OF THE INVENTION and reflector structures in which arectangular or square pattern of light is formed by canting, filting, ormodifying portions of a conventional reflector so that the resultingreflector has a non-circular cross section. Projected images or fieldsfrom the reflector segments are caused to be defined and overlap eachother to form a desired geometric pattern of light of substantiallyuniform intensity thereacross. The lamp structure shown in thatapplication has met with commercial success and, for example, ispresently being used for the reading light lamp in the Boeing 747aircraft/ However, it does require that the reflector portion of thelamp be especially modified, but has the advantage that no special lensis required, thereby creating a light-weight and effective projectorconstruction.

SUMMARY OF THE INVENTION The present invention is directed to anotherarrangement by which a rectangular or square pattern or field of lightdefined by mutually overlapping light segments, can be formed from aconventional non-collimating circularly continuous parabolic orelliptical reflector. For example, the reflector may be of theconventional parabolic form in which the filament of the bulb has beendisplaced either ahead of or behind the focus to form a diverging,spreading filament image and light pattern. on the other hand, thereflector may be formed as a revolved ellipse that is, one in which acircularly continuous reflector has been generated by revolving asegment of a tilted ellipse about an axis. Examples of the generation ofsuch reflectors are disclosed in the above-identified copendingapplication, and another example of such reflector is disclosed, forexample, in Nordquist U.S. Pat. No. 2,602,135 of July I, 1952. Revolvedellipse reflectors are in common use where it is desired to provide aspreading pattern or field of light.

With either type of reflector described above, I employ a prismatic lenswhich comprises individual arcuately arranged prism segments. Each prismsegment is arranged to intersect a corresponding segment, such as aquadrant, of light from the reflector and to displace this segmentlaterally with respect to a center axis. The lateral displacement causedby the prism segment is similar, in effect, to that caused by themodified reflectors of copending application Ser. No. 724,688 now US.Pat. No. 3,588,493.

Each prism segment forms a corresponding segment of the light patternwhich is correspondingly displaced so that a mutually overlapping lightpattern or field is formed of substantially uniform intensity from sideto side or diagonally from corner to corner. When four equal 90 segmentsare employed, a rectangular pattern is formed in which the sides of thepattern were formerly radii of the unmodified circular pattern from thereflector. Such square pattern is smaller than the unmodified pattern bya factor of pi.

The individual prism segments of the lens may be formed with the thickerportion at the periphery of the lens or with the thicker portion at thecenter of the lens, depending upon the reflector and position of thelight source. When the the axis of tilt of the elliptical reflector issmall, the light rays from any side of the reflector will cross througheach other and will become displaced on opposite sides of the centerline at a given field plane. In this case, the thicker portions of theprisms will be at the periphery of the lens to provide the requiredimage displacement. On the other hand, if the elliptical reflector isformed with a revolved ellipse in which the focal point of the ellipsefor any cross section thereof, lies on a more substantially tilted axis,individual rays from any segment thereof will converge at a narrowerangle and the individual segments from such a reflector, at a givenfocal length, may be brought together into the desired mutuallyoverlapping relation by a prismatic lens in which the segments of theprism have their thicker portions at the center of the lens.

If a parabolic reflector is used in which the filament is displacedahead of the focus, a prismatic lens is used in which the thickerportions are at the periphery. On the other hand, if the filament ispositioned behind the focus to form a diverging and non-inverted-patternof light, then a prismatic lens is used in which the thicker portionsare at the center of the lens. Any embodiment disclosed herein, it iswithin the scope of the invention to reduce the overall thickness of thelens by the Fresnel technique.

It is accordingly an important object of the invention to provide asimplified projection and lens arrangement by which a uniformrectangular or square pattern of light is formed from a circularlycontinuous reflector.

Another object of the invention is the provision of a projector having aprismatic lens formed in four essentially equal quadrants or segments,each segment defining an individual prism which is essentially identicalto that of the adjacent prism, and which are effective with a reflectorto form a pattern of light having a corresponding number of straightsides.

A further object of the invention is the provision of a projector andlens assembly-which may be used to form a rectangular or square patternof light which pattern is smaller than the pattern developed by thereflector alone and which is of generally uniform intensity across thepattern.

Another object of the invention is the provision of a projector and lensas outlined above, which produces a square pattern of light fromparabolic or elliptical reflectors.

These and other objects and advantages of the invention will be apparentfrom the following'description, the accompanying drawings and theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a diagram of a reflector andthe light pattern formed by the reflector to which the present inventionis applied;

FIG. 2 is a view looking into the reflector;

FIG. 3 is a view of the system of FIG. 1 showing the manner in which alens quadrant modifies a portion of the light from the reflector;

FIG. 4 is a further diagram of the reflector and lens combination ofthis invention showing a rectangular pattern formed thereby;

FIG. a is a plan view of the lens used in the embodiment of FIGS. l4;

FIG. 5b is a side view of the lens;

FIG. 6 is a further diagram showing another form of reflector to whichthe invention may be applied and the pattern produced by such reflector;

FIG. 7 is a diagram showing a pattern as formed by a modified lens ofthis invention;

FIG. 8a is a plan view of the modified lens; and

FIG. 8b is a side view thereof.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring to FIG. I, an ellipticalreflector is illustrated generally at 10, and a light source, which maybe a filament bulb, is illustrated at 12 positioned within the reflector10. The reflector 10, as shown, is of the tilted ellipse type in whichthe surface 14 of the reflector is formed as a tilted and revolvedsegment of ah ellipse. The foci at the filament l5 and at the point 16lie on an inclined axis 17. The reflector is generated by revolvingabout the center line so that the locus of all points forming thesecondary focus 16 form a circle with its center on the center line.Depending upon the inclination of the axis 17, the light field 18 may beeither broad or narrow. The concentric circles or rings illustrated at20 are provided merely for the purpose of reference points and, in fact,may actually comprise brighter rings of light due to the rotation of thefilament image, when a coil-type axial filament is employed as thesource 12. However, for the purpose of this invention, the concentricrings may be considered as representing the reflected images from thereference points 1, 2, 3, 4 and 5 as shown on the reflector and asdesignated on the field 18.

In FIG. 1, the images have crossed over each other so that light fromthe quadrant A of the reflector has passed through inversion at thefocus 16 and occupies a diametrically opposite position illustrated bythe same reference points 5, 4, 3, 2', and 1 on the light field.Similarly, the light from the quadrants B, C and D occupy reversedpositions shown by the corresponding letters on the light field. Whilethe light field 18 is shown-as having been developed by a revolvedelliptical reflector, essentially the same light pattern for the purposeof this invention may be developed by a conventional parabolic reflectorin which the filament point has been displaced forwardly of the focus,so that the reflector becomes, in effect, an image-inverting reflectorwith respect to the filament image.

. Referring to FIG. 3, a prism is shown as being interposed'between thefocal point 16 and the open side of the reflector 10. In this instance,the thicker portion of the prism is at the peripheral edge. Since theprism bends the light toward its thicker side, if the prism 25 is madeas a 90 segment of a circle, corresponding to the segment A of FIG. 2,it may be chosen with a taper sufficient to shift the quadrant A of thelight field with respect to the center line a distance approximatelyequal to the radius R of thepattern l8 multiplied by the square root of2. The sides 26 and 27 of the moved segment, which equals the radius R,would form two of the sides of the completed square. Thus, if a lens ismade up of four 90 prism segments 25, one for each quadrant A, B, C andD of the lens 10, the corresponding 90 segments of light would be formedinto a mutually overlapping pattern illustrated generally at 30 in FIG.4.

Such a composite prismatic lens for this purpose is illustrated at 32 inFIGS. 4 and 5 in which the individual arcuate segment 25A, B, C and Dare joined along common radii, each comprising a segment of a completecircular lens. The composite pattern 30 is made up of the four displacedpattern segments A, B, C and D; and the perimeter lines comprise formerradius lines of the pattern 18. If desired, a Fresnel technique may beapplied to the lens 32 to reduce its thickness. The lens 32 will performessentially the same with the tilted elliptical reflector shown in FIG.1 in which there is image reversal, and with a parabolic reflector inwhich the filament has been moved forward of the focus so that imagereversal occurs.

The embodiment of the invention shown in FIGS. 6-8 is one in which thethicker portion of the prism lens is located at the center of the lens.This may be a more desirable arrangement in order to reduce the overallweight of the lens as the mass of the lens would be less as compared toan embodiment in which the thicker part of the prism is at thecircumference. Looking first at FIG. 6, a revolved elliptical reflector50 is tilted along an axis 52 which is at a rather substantial angle tothe center line. In this instance, a circular field 58 is formed priorto crossover of the images from the individual reflector segments A, B,C and D. Again, reference points 1 through 5 are shown on the surface ofthe reflector 50 and the corresponding points are shown on the field 58.Thus, a reference point 5 in the embodiment of FIG. 6 occupies thecenter of the field 58 whereas in the embodiment of FIG. 1 it occupied aposition on the periphery of field 18. The reflector 50 may also be aparabolic reflector but one which the light source or filament has beendisplaced inwardly of the focus, rather than outwardly, to form aspreading with respect to each quadrant of the lens. This results in abending of the light inwardlytoward ,the center line and forms the fullyoverlapping image or'pattern 64 as shown in FIG. 7. The pattern 64 isessentially identical in appearance and shape to that of the pattern30,-ex

cept that the light making upthe pattern is from reversed positions withrespect to the reflector. This pattern 64 is also essentially uniform inintensity throughout, has a sharp fall-off of light outside the pattern,and is smaller than the field 58 by a factor of pi. Again, as in thecase of the lens 32, a Fresnel technique may be applied to the lens toreduce its overall thickness.

A parabolic reflector in which the light source is displaced axiallyinwardly of the focus is not image inverting. Since there is no crossingover of the reflected light with respect to the center line of thereflector, the pattern formed is very much like that of pattern 58 andaccordingly essentially the same lens 60 with prism segments having thethicker portion oriented at the center line or axis may be used forquadrature image displacement into a mutually overlapping pattern 64.

Either of the embodiments shown may be used with advantage in sealedbeam lamps and the like, in which be desired to form each lens segmentas a series of 5 small FResnel prisms, to reduce overall thickness.

While the forms of apparatus herein described constitute preferredembodiments of the invention, it is to be understood that the inventionis not limited to these precise forms of apparatus, and that changes maybe made therein without departing from the scope of the invention.

What is claimed is:

1. A reflector and lens projecting assembly adapted to project anessentially square pattern of light from a lamp and a generally circularreflector, comprising a source of light, a circularly continuousprojecting reflector associated with said source to project a diffusedgenerally circular pattern of light therefrom, and a lens interposed tointercept reflected light from said reflector having four essentially 90segments, each said segment consisting of a prism positioned tointercept a corresponding segment of reflected light, and effectinglateral displacement of a corresponding segment of said pattern to forma composite essentially square light pattern in which each side thereofis approximately equal to a radius of said circular pattern formedwithout the lens.

2. A reflector and lens projecting assembly adapted to project anessentially square pattern of light in combination with a light sourceand a reflector, comprising means defining a source of light, acircularly continuous projecting reflector positioned with respect tosaid light source to project a non-focusinggenerally circular pattern oflight therefrom, and a circular lens interposed to intercept reflectedlight from said reflector, said lens having four arcuate segments eachdefining an individual prism, each segment being positioned to interceptlight from a corresponding segment of the reflector and to effectlateral displacement thereof resulting in a mutually overlapping squarepattern of light in which each side of the resulting square isapproximately equal to a radius of said circular pattern.

3. The assembly of claim 2 in which said circular pattern when formed onan image plane, in the absence of said lens, is one in which the imagesfrom one side of the reflector cross over, and are inverted, withrespect to the center axis of the reflector, and in which each saidprism segment of the lens is formed with its thicker portion at the lensperiphery.

4. The assembly of claim 2 in which said circular pattern, when formedon an image plane in the absence of said lens, is one in which theimages from one side of the reflector are formed on the same side of thecenter axis of the reflector, and in which each said prism seg ment ofthe lens has its thicker portion substantially at the center of thelens.

5. The assembly of claim 2 in which said reflector is parabolic.

6. The assembly of claim 2 in which said reflector is elliptical.

7. The assembly of claim 2 in which each said lens segment displaces itsassociated said image a distance of approximately the radius of the saidcircular pattern multiplied by the square root of 2. j

8. lens element for use with a pro ecting reflector comprising fouressentially equal and identical prismatic segments, each said segmentbeing symmetrically positioned with respect to each other with thethicker portion of each segment being positioned at the lens center, andeach said segment having one surface thereof lying in a plane commonwith a corresponding said surface of each of said other segments.

9. A lens element for use with a projecting reflector comprising fouressentially equal and identical 90 prismatic segments, each said segmentbeing symmetrically positioned with respect to each other with thethicker portion of each segment being positioned at the lens periphery,and each said segment having one surface thereof lying in a plane commonwith a corresponding said surface of each of said other segments.

1. A reflector and lens projecting assembly adapted to project anessentially square pattern of light from a lamp and a generally circularreflector, comprising a source of light, a circularly continuousprojecting reflector associated with said source to project a diffusedgenerally circular pattern of light therefrom, and a lens interposed tointercept reflected light from said reflector having four essentially90* segments, each said Segment consisting of a prism positioned tointercept a corresponding segment of reflected light, and effectinglateral displacement of a corresponding segment of said pattern to forma composite essentially square light pattern in which each side thereofis approximately equal to a radius of said circular pattern formedwithout the lens.
 2. A reflector and lens projecting assembly adapted toproject an essentially square pattern of light in combination with alight source and a reflector, comprising means defining a source oflight, a circularly continuous projecting reflector positioned withrespect to said light source to project a non-focusing generallycircular pattern of light therefrom, and a circular lens interposed tointercept reflected light from said reflector, said lens having fourarcuate segments each defining an individual prism, each segment beingpositioned to intercept light from a corresponding segment of thereflector and to effect lateral displacement thereof resulting in amutually overlapping square pattern of light in which each side of theresulting square is approximately equal to a radius of said circularpattern.
 3. The assembly of claim 2 in which said circular pattern whenformed on an image plane, in the absence of said lens, is one in whichthe images from one side of the reflector cross over, and are inverted,with respect to the center axis of the reflector, and in which each saidprism segment of the lens is formed with its thicker portion at the lensperiphery.
 4. The assembly of claim 2 in which said circular pattern,when formed on an image plane in the absence of said lens, is one inwhich the images from one side of the reflector are formed on the sameside of the center axis of the reflector, and in which each said prismsegment of the lens has its thicker portion substantially at the centerof the lens.
 5. The assembly of claim 2 in which said reflector isparabolic.
 6. The assembly of claim 2 in which said reflector iselliptical.
 7. The assembly of claim 2 in which each said lens segmentdisplaces its associated said image a distance of approximately theradius of the said circular pattern multiplied by the square root of 2.8. A lens element for use with a projecting reflector comprising fouressentially equal and identical 90* prismatic segments, each saidsegment being symmetrically positioned with respect to each other withthe thicker portion of each segment being positioned at the lens center,and each said segment having one surface thereof lying in a plane commonwith a corresponding said surface of each of said other segments.
 9. Alens element for use with a projecting reflector comprising fouressentially equal and identical 90* prismatic segments, each saidsegment being symmetrically positioned with respect to each other withthe thicker portion of each segment being positioned at the lensperiphery, and each said segment having one surface thereof lying in aplane common with a corresponding said surface of each of said othersegments.